Well, the subtitle of the article is, "The problem of cross-genre covers." (emphasis added). Johnny Cash's covers are pretty much all spectacularly done.

Maybe it's also because Cash had a background in genres (including folk & gospel) that tend to play all sorts of songs written by others as well as themselves, and often call them "traditional" or "standards" rather than "covers"? It's no secret that Dylan had a folk background, too.

So, I posit that's why neither Dylan nor Cash got a mention in this article. They both did multi-genre covers well, hence no "problems." Maybe this phenomenon is more of a rock-rap thing? Perhaps country, folk, gospel, bluegrass, to name a few, tend to be less proprietary in identifying a song as "belonging" to an artist, and are more likely to do a good cover?

Thoughts, anyone?